1. Field of the Invention
The present invention relates to a method for writing servo onto a disk of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads can magnetize and sense the magnetic fields of the disk to write and read data, respectively. The heads are coupled to a pivoting actuator arm that has a voice coil motor.
Data is typically stored on tracks that extend radially across the disk surfaces. The voice coil motor can be energized to pivot the actuator arm and move the heads to different track locations. Each track is typically divided into a number of sectors. Each sector contains at least one data field.
To accurately locate the heads relative to the disk tracks, each track contains a plurality of servo fields. Each servo field typically contains a plurality of servo bits that are read to create a position error signal (“PES”). The PES is used in a servo routine to center the heads relative to the centerlines of the tracks. It is desirable to write data when the heads are located on the center of the tracks so that the writing process does not corrupt data on adjacent tracks.
The servo bits are typically written as part of the manufacturing process of the drive. There are various techniques for writing servo onto the disks. For example, some manufacturers use a dedicated servo writer machine that is located in a clean room. The servo writer may have a spindle motor and a separate head assembly. Disks are loaded onto the spindle motor and the head assembly writes the servo information directly to the disk surfaces. The spindle motor rotates the disks during the servo writing process.
After the servo writing process is completed the disks are unloaded from the spindle and assembled into a hard disk drive. Alternatively, some servo writers are configured to write onto the disk surfaces after the disks are assembled into a drive assembly. The spindle motor of the drive assembly rotates the disks during the servo writing routine.
Rotation of the disks creates a flow of air across the disk surfaces. The air flow cooperates with air bearing surfaces of the heads to create air bearings between the heads and surfaces of the disks. The air bearings prevent excessive mechanical wear between the heads and the disks.
Unfortunately, the flow of air also creates a mechanical vibration within the disk drive. The vibration can cause undesirable movement of the heads relative to the disk. Such movement of the heads during a servo writing routine may create repeatable run-out (“RRO”) and non-repeatable run-out errors (“NRRO”) in the servo PES. The errors may increase the seek and access times required to read and write data onto the disks. It would be desirable to reduce the vibration induced errors created by the flow of air during a servo writing routine.